The present disclosure pertains in general to electronic circuit breakers and, more particularly, to an electronic circuit breaker operating under programmed control and having a variety of self-test operations integrated into the operating sequence of the switching device or circuit breaker.
Recently, designers of switching devices and circuit breakers have introduced fault interrupting circuits into the operational features of these devices. The added features introduce another level of protection for the user by tripping the device responsive to another set of common faults which were not detectable in the earlier circuit switching designs. For example, a ground fault circuit interrupter (GFCI) responds to a net imbalance in the current flowing through the line and neutral conductors to a connected load device. If the current differs by more than a few milliamps, a leakage current path may exist between one of these conductors and accessible surfaces or earth ground, resulting in a possible shock hazard. As another example, an arc fault circuit interrupter protects against arcing faults, which may ignite combustible materials in the vicinity of the arc fault. These types of fault interrupter devices are typically tested by the manufacturer, and they also offer and include a push-to-test button on the device for the user to operate a test. It would be much more useful to be able to test these circuit interrupting devices periodically and to test them in situ while in use to maximize the assurance that they are functioning effectively, it would also be advantageous to provide this additional test capability at little or no increase in cost.
A method is disclosed for testing a circuit switching device or circuit breaker having separable contacts operable under processor control to control power to a circuit responsive to at least one of a plurality of fault conditions, comprising the steps of controlling the switching device during a sampling cycle, to input one or more operating parameters sensed in the circuit to an analog-to-digital (A/D) converter for measurement wherein the operating parameters enable detection of the fault conditions; determining whether to read a select one of the operating parameters from an output of the A/D converter into a first memory; and reading pre-determined parameter values from a second memory into the first memory during the sampling cycle instead of the operating parameters read from the A/D converter if a self-test has been invoked during the sampling cycle.
In another aspect of the present disclosure, an apparatus for testing a circuit switching device such as a circuit breaker having separable contacts for controlling power supply to a circuit responsive to at least one of a plurality of fault conditions, comprising a processor having an A/D converter with parameter inputs coupled thereto and operating according to a periodic sampling cycle to measure operating parameters of the circuit and detect the fault conditions occurring therein; a first memory coupled to the processor for storing the operating parameters of the circuit output from the A/D converter during measurement by the processor for use in determining the fault conditions; and a second memory coupled to the processor and having stored therein predetermined parameter values for substitution for the measured parameters when a self-test is being invoked during a sampling cycle.